1. Field of the Invention
The present invention relates to a flat panel display, more particularly, to an organic electroluminescent display device capable of preventing inline short and voltage drop on a power supply layer by having the power supply layer and an anode electrode layer formed simultaneously and on the same layer while forming the power supply layer on a different layer than on the layers the data and gate lines are formed.
2. Description of Related Art
Typically, each pixel of an active matrix organic electroluminescent display device includes a switching transistor, a driving transistor, a capacitor, an EL (or an electro-luminescence) device, and a power supply line. The power supply line delivers common power (Vdd) to the driving transistor and the capacitor. Preferably, a common power should be uniformly supplied to each and every pixel in the matrix to obtain uniform luminance for each pixel. The design of the power supply line plays a role in controlling current flowing to each of the EL devices in the matrix through the respective driving transistor.
The EL device is made up of an anode (or pixel) electrode, a cathode electrode and an EL (or light emitting) layer. The EL layer is of an organic composition that emits light when current is applied. The switching transistor and the driving transistor are thin film transistors (or TFT's).
A plurality of conductive layers are used in an active matrix organic electroluminescent display device to form a gate line, a gate electrode, a data line, a source/drain electrodes for the TFT's, a power supply layer, an anode electrode, etc., wherein insulation layers such as gate insulation film, interlayer insulation film and passivation film is interposed between the conductive layers so that the conductive layers are electrically isolated from each other.
In an electroluminescent display device, it is preferable to form the conductive layers so that they all remain electrically isolated from each other and do not accidently short with one another. It is also preferable to construct the power supply line in such a fashion that all pixels within the matrix receive the same amount of power at the same voltage so that there is no voltage drop along the power supply line. In other words, the power supply line must be free of any voltage drops within the conductive power supply line. Further, it is preferable that the power supply line is formed so that it is sufficiently separated from the data, gate and other conductive lines to prevent the possibility of an accidental inline electrical short. Further, it is preferable that the structure for the electroluminescent display be efficiently produced, requiring as few process steps to make, to reduce the costs of manufacture. Therefore, when possible, it is desirable to combine process steps.